The invention relates to an electron gun for heating, fusing and vaporizing purposes, having a high-voltage part, an electron emitting cathode, at least one beam forming electrode associated with the cathode, an accelerating anode, and a beam guiding tube extending in the direction of the beam path and surrounded by a jacket tube, in which gun an electromagnetic lens and at least one deflection system are disposed in the chamber formed between the beam guiding tube and the jacket tube.
An electron gun of the kind described above is disclosed in German Pat. No. 1,248,175, which has resulted in a considerable improvement of the gun systems existing in its time, but which is in need of improvement. In this known gun, the space between the jacket tube and the beam guiding tube, in which the electromagnet lens and the coils of the deflection system are located, is traversed by a coolant (water) to prevent the thermal overloading of these coils. This necessitates an appropriate encapsulation of the coils, since the coolant might otherwise destroy the insulation and corrode the terminals. At the same time the jacket tube and the beam guiding tube are united inseparably with one another, i.e., the space or chamber containing the electromagnetic lens and the deflection system is hermetically sealed. This is necessary mainly because a positive guidance of the coolant must be brought about by constructional measures which dictate the internal structure of the system. Any subsequent modification of the system by the partial replacement of parts associated with the optical control of the electron beam is impossible.
In the known electron gun, furthermore, the jacket tube and the beam guiding tube are joined to the high voltage insulator of the gun by a sleeve-like part which is provided with a lateral nipple for connection to a vacuum pump system. Although a vacuum that is adequate for the reliable continuous operation of the system can thus be provided even in the area of the cathode and the beam forming electrode by means of an evacuating system separate from the rest of the installation, nevertheless it is no longer easily possible to install such a gun in a vacuum chamber without a separate vacuum connection, since the relatively narrow connecting nipple would in this case impair the reliability of the evacuation of the cathode area. The creation of correspondingly large openings in the sleeve-like part would, on the other hand, impair the strength of the known construction.